In large parts of the US you do not need to water you lawn as rain will provide all the water you need. You never need to put weed killer on a lawn, just a regular mowing (ideally with a reel push mower) will be enough. Most of what people call weeds are harmless biodiversity. In some parts of the US lawns are native grass, though that isn't common.

Understand that most people over manage their lawns. You can get your lawn a little more green (the color, not the environmental green) with excess water and chemicals. They are not needed at all though.